Group 16 - DeWalt 4 1/2 in Angle Grinder Gate 4

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In this phase of the project our group completed our reverse engineering process by reassembling our product and gathering information from the reassembly process. In Project Management our group describes how we have worked through the challenge presented in Gate 3, as well as discussing why our current group structure has prevented further challenges from arising. Once this had been completed our group did the reassembly and created a step-by-step process so that our product could be reassembled without significant prior knowledge of the product. After this our group analyzed the helical bevel gear, one of the primary mechanisms in our product, and considered both its purpose and the equations governing its motion. Our group then recommended three system level design revisions that would improve the overall functionality of the product. All of these can be found under Product Archaeology. Lastly, in Conclusions our group considered all of the information we have gathered over the course of this project in order to make detailed conclusions about the original design of our product.

Project Management

As described in Gate 3, our group's last remaining issue is the attendance of one group member. This member did not attend for the meeting where we divided the assignments for this gate, thereby preventing him from taking on or contributing to any of the gate components. Several times now he has been told when and where the group will be meeting, but he has failed to attend or give a valid reason for missing. Our group divided the work in such a way that we will still complete this gate efficiently, even without this member's help. For Gate 3 this method proved workable, as the workload was not too severe for four people to complete. We therefore have avoided assigning this member important tasks (or any tasks in this case) and will be mitigating the problem through the same means used before. This solution has been an effective method of preserving the overall project quality without severely impacting any of the other members.

Besides this attendance problem, our group has no remaining internal problems. All of the solutions provided since Gate 2 (and listed below) have been effective:

  • Not knowing how to use the wiki: Our group's functional knowledge of the wiki has been enough to allow effective technical communication because of the previous steps taken to learn how the wiki works.
  • No out of class meetings: While our group does not have regularly scheduled meeting time, we have done well at getting most of the group together when the Project Manager gives a couple days' notice. This has allowed our group to adapt and function in a way that would not be possible if all communication was via email.
  • An unevenly distributed workload: With the exception of the aforementioned member, the work has been divided as fairly as possible, with considerations for the amount of work involved in any part taken into consideration. For this gate, the instructor provided a breakdown of the point allotments for each section, which aided our group in assessing how much time each part would entail. We thus were able to come up with a fair distribution of work.

Product Archaeology

Product Reassembly

Difficulty Scale

In order to describe the difficulty of each step during the reassembly process our group will use the classifications outlined in Table 1. These classifications don't just consider the time involved in any given step, but also take into account the tools required, accessibility of the parts, required force, and overall intuitiveness. In addition, some of the steps may have required creative approaches as all of the factory tools and machines would not have been accessible when reassembling by hand. Any of these creative approaches are listed under the Challenges section, as they would be necessary for an average user to reassemble the product while only using household tools.

Table 1:Difficulty Ratings for the Reassembly Steps
Difficulty Description Example
Easy This step was completely intuitive, required minimal skill, involved no excessive force, and took a small amount of time. The average user would not need detailed instructions to perform this step. Screwing a nut or screw back into its original location
Moderate This step required some planning to perform, involved a difficult hand or tool positioning, needed some force but could still be done by the average person by hand, and/or took a greater amount of time than an Easy Step. A description of the step would be very helpful for a person who had no prior knowledge of the product. Forcing a series of parts onto a shaft in the correct order.
Challenging These steps were very difficult to perform, either requiring fine work in a hard to reach place, large amounts of force that cannot easily be applied by hand, and/or requiring a creative approach in order to reassemble the part. In addition to a general description of the step in Table 2, Challenging steps will be described in greater detail in the Challenges section. Replacing a part that was originally shrink fitted on

Reassembly Instructions

The information in Table 2, in combination with the Challenges section, is intended to give a set of full instructions so that a user not familiar with the product could easily reassemble it. In addition, the original factory methods for assembly are described, as well as comparisons to the disassembly process. These are intended to highlight the ideal methods for reassembly and point out key deviations from the disassembly process for individuals who have greater resources or completed the disassembly themselves respectively. Lastly, pictures of the product at the end of each step are provided so the user can check their work and make sure they have connected the right parts.

  • Before beginning reassembly, the following tools will be needed
    • Phillips-head Screwdriver
    • Torx Drivers:T-5, T-10, T-15
    • Needle-nose Pliers
    • 3/8" Crescent Wrench
    • 10 mm Socket
    • Hammer
Table 2:Instructions for Reassembly
Step Tools Description Difficulty Original Assembly Disassembly Comparison Image
1 None Slide the electromagnet into the main housing with the wires towards the bottom. Each wire must go through one of the holes at the bottom of the housing along with the wire nearest to it. The electromagnet will be a very tight fit, and will require a lot of pressure. Challenging A machine would have fit through the holes and pulled the wires out while a press simultaneously forced the magnet into the housing. This will be the reverse of the disassembly process, however feeding the wires through the two holes will be a challenge that was not present before. This will significantly increase the difficulty, because the wires must be controlled while the magnet is being pressed in.
2 Needle Nose Pliers Use the needle nose pliers to take the shorter of the two wires from each electromagnet side and connect them to the lead above the brush spring. Easy This step would have been done by hand, the same way in the factory. This is the reverse of disassembly. No significant deviations.
3 10 mm Socket, Hammer Take the bottom shaft bearing (it has a slightly larger interior hole than the top shaft bearing) and replace the rubber coating. Then force the bearing onto the metal nub at the bottom of the drive shaft. It must be forced all the way down (not just to the nub). To do this, place the bearing over the nub, and then place the socket on the bearing, with the drive shaft firmly secured. Then use the hammer to tap the socket until the bearing is pressed onto the nub. Challenging This part was shrink fitted on in the factory This is the reverse of disassembly but will be more difficult because a instead of just forcing the bearing off, it must be controlled and the drive shaft must be stabilized as it is forced back down.
4 T-5 Torx Driver, Needle Nose Pliers Realign the plastic brush support over its hole, and screw the Torx screw in to secure it. Now pull the spring back and place it on the plastic ledge of the housing. Then insert the brush into its holder, sliding the wire through its hole. Use needle nosed pliers to connect the lead to the nearest metal slot. Repeat for other side. Moderate A machine would have moved the pre-assembled brush into position and then screwed it down. The leads would then be connected by hand at a later point. (All wires would be connected at once) This is the reverse of disassembly. No significant deviations
5 10 mm Socket, Hammer, 3/8" Crescent Wrench Slide the fan baffle on the top of the drive shaft (concave side down). Then align the bearing and use the method described in Step 3 to force it on. Next, push the pinion onto the shaft. It should be tight, but can be forced by hand. Finally, screw the nut on with the 3/8" crescent wrench. Challenging All of this assembly would have been done by machine in a factory. It would have followed the same steps except that the bearing would have been shrink fitted on. This is the reverse of disassembly. The only notable difference is for replacing the bearing, which is already described in Step 3.
6 None Slide the narrow end of the switch bar through the rectangular hole at the base of the housing. Once the narrow end reaches the switch hole, press the plastic switch against the switch bar in order to clip it back on. Easy A machine would have followed the same process in order to slide the bar in and then quickly press the plastic switch on. This is the reverse of disassembly. No significant deviations
7 T-5 Torx Driver Slide the black retaining bracket into the housing and then screw it down with the four T-5 screws. Place the drive shaft assembly inside the bracket (bottom first) and slide it in until the fan baffle is flush with the top of the housing. Easy A machine would have followed the same process to assembly the part in a factory. This is the reverse of disassembly. No significant deviations.
Fan Baffle.jpg
8 T-10 Torx Driver Place the gearbox on top of the housing. It will not fit unless the pinion is turned to align with the helical gear. Then screw the four T-10 screws down to secure the gearbox. Moderate This part would have been attached and secured using a machine in a factory. Because of higher control of the part, the machine would have been set to make sure the helical gear aligned with the pinion the first time. This is the reverse of disassembly. No significant deviations.
9 Phillips-head Screwdriver Place the gear cover on the back of the gearbox and secure it by screwing the four screws in. Easy A machine would have done this step in factory. This is the reverse of disassembly. No significant deviations.
10 Needle Nose Pliers, Phillips-head Screwdriver Place the half of the lower housing with five holes on the bottom of the main housing. It has a groove that will allow the switch bar to slide in. Now place the electronic switch in the open space (button towards the bar). Then take the long wires from the electromagnet and connect them to the leads at the bottom of the switch with needle nose pliers. Then take the two wires from the power cord and connect them to their respective sides of the switch (black to black, white to white). Lastly, screw down the two screws on the electronic switch to secure all of the wires in place. Moderate All of this would have been done by hand in a factory. These steps would be performed at the same time that the leads from the brushes were connected. This is the reverse of disassembly. No significant deviations.
11 T-10 Torx Driver Place the second half of the lower housing on top of the first half, and secure the five screws that hold them together. Easy A machine would have performed this step in a factory. This is the reverse of disassembly. No significant deviations.
12 Phillips-head Screwdriver Place the guard clamp around the forward ring of the gearbox, and bring the two ends of the clamp together. Next, push a screw through the non-threaded end of the clamp, and then use the screwdriver to screw it into the other end. The two ends must be held together close to the connection while the screw is aligned and screwed in, which can be difficult for only one person. Challenging In a factory a machine could easily perform the steps described above because it is not limited to just two "hands". It could therefore hold the guard together and screw the screw in with ease. This is the reverse of disassembly, however it is more challenging because the screw and two ends of the guard clamp must all be aligned at once, while the screw is simultaneously screwed in. This is much more difficult than just unscrewing the screw as was done during disassembly.
13 None Slide the backing flange over the small shaft coming out of the gearbox. Next, slide the clamp nut partway on, and then screw it on until it is tight. Easy This step would have been done by a machine in a factory. It would have used the same steps listed. This is the reverse of disassembly. No significant deviations.


Our group faced challenges with reassembly for steps 1, 3 and 5 (same problem), and experienced some difficulty with step 12. These challenges and our methods for overcoming them are listed below.

  • Step 1: What made step 1 challenging was that while the electromagnet is being pressed in four wires, which cannot be touched during this process, must slide through two small holes, which are located halfway between each wire in the respective pair. The only way our group could get the wires to align properly was to use duct tape to hold each pair together, and then try to align the two "bundles" of wires with the holes they needed to slide through. The duct tape was then removed, and the reassembly proceeded as described.
  • Step 3 and 5: As described in Table 2, our group had to use a socket and hammer to force both bearings back on. These were difficult to remove because they were shrink fitted on, but the reassembly was even more difficult. The hammer was necessary to provide enough force to push the bearing on, while the socket allowed the force to be distributed evenly to the entire bearing, thereby preventing it from dis-aligning or breaking.
  • Step 12:What made step 12 a challenge was that the multiple tasks, pinching the clamp ends, sliding the screw in, and turning the screwdriver, required "three hands" in order to complete. For our group this was easily solved by getting someone to help out, but for someone working alone it would have been very difficult to replace the guard due solely to the awkward hand positioning.


Bevel Gears.jpeg
Spiral Gearing.jpg
Helical Gear.JPG


The Technical name for our mechanism is a Helical miter differential.

  • The smaller gear drives the larger gear making this mechanism a miter gear.
  • The helical cut gear pattern lessens vibration and extends tool lifetime.
  • The 90 degree change in direction of the output and input shafts classify this mechanism as a differential.


  • Change power output direction 90degrees


  • The unique shape of the gears allows for a 90 change in direction of the two gears axis.
  • The smaller gear drives the larger gear which is connected to the output shaft.

Governing Equations

N = number of teeth on pinion

n = number of teeth on gear

a = angle of teeth (deg)

Pp = power at pinion shaft (kw)

Np = rotational speed of pinion shaft (rev/min)

Dp = diameter of pinion pitch circle (mm)

Mp = Torque on pinion shaft

  • Mp = [60/(2 x 3.14x Np)] x Pp

Ft = Tangental force on pinion

  • Ft = (2000 x Mp)/Dp

Fs = Seperating force

  • Fs = Ft x tan (a)

e = Pitch angle of pinion

  • e = tan^-1 (N/n)

Fp = Pinion Thrust

  • Fp = Fs x sin (e)

Fg = Gear thrust

  • Fg = Fs x cos (e)

(All information for this part taken from 1800 Mechanical Movements. See References for more information)

Design Revisions

With the exception of the design changes in Gate 3, our product does not have any significant flaws. The design revisions for this gate were therefore not intended to fix problems, but instead to improve the functions of the grinder that are already in place.

Changeable Gear Box

The attachment slides onto the grinder handle.
The attachment and handle interlock.

Multiple Attachments By making the housing of the grinder have a steel sleeve that the gearbox head and several other attachments mate with we can allow the user to adapt the tool with any type of attachment for various applications. Since the user never has to change tool housings they can cut down on weight and time. It is quick and easy to change a tool head rather than finding the new tool and plugging it in. The target audience would be for the average home tool enthusiast.

GSEE Factors

  • Global

No new global factors.

  • Societal

The new more intuitive design will make it easy for the user to swap out tools.

  • Economic

Now a user can expand their tool collection at a lower cost than before.

  • Environmental

No new environmental factors.

Advantages and Disadvantages

The primary advantage of this design revision is that it will increase the already impressive versatility of the angle grinder. Through the use of different gear heads it will be possible not only to perform grinding functions at different angles, but also to perform functions that currently require a completely different tool. For example, through the use of a gear head that utilizes a slide crank it may be possible to use the angle grinder as an impact wrench. These additional functions would require more research to completely flesh out, but we presume that it will be cheaper than buying separate tools for these functions because all of the angle grinder's attachments will run off the same motor and drive shaft. A secondary advantage of this design revision is that it will be lighter and more convenient for users to take their one angle grinder and attachments to a work site than to bring a collection of very specific tools.

The only significant disadvantage of this product is the increase in material (and by extension, cost)will make the angle grinder's price rise. While it will be cheaper for a consumer to buy the new angle grinder and attachments than to buy all tools separately, there will be difficulty entering the market because many experienced professionals probably already own most of the additional tools they need. If this is the case, those professionals will opt for competitor's angle grinders just because they are cheaper. This problem will fade over time however, as people entering the market for the first time or those who need to replace many of their aging tools will opt for the revised DeWalt angle grinder because of its superior versatility.

Adjustable Handle

The blue arrows show the positions where the handle will be able to lock in place after redesign

For our next design revision we propose replacing the current handle with one that can rotate around the grinder in 45 degree increments. Currently, the handle can only be placed in two locations: one for left handed people, and one for right handed people. Either handle location is parallel to the grinding surface, which requires the user to hold the handle at an awkward position in order to use the grinder. Besides the discomfort this causes the user, holding the grinder at an awkward angle will also decrease the overall precision. By adding a truly adjustable handle system we will improve the overall functionality of the grinder by allowing the user to easily hold it at whatever angle they desire for the current job.

This system will work by placing a track along the steel sleeve mentioned in the previous revision. At every 45 degree interval the track will have a hole that the handle can lock into. The handle will be attached to the track by a spring. In order to adjust the handle, the user will simply pull on the handle, removing it from its current hole, slide it to the desired position, and release it. The spring will then pull the handle down into the current hole, re-securing it for work.

GSEE Factors

The primary concerns behind this new design will be global, societal, and economic.

Global Factors: The system design will be very intuitive, as the user just pulls on the handle and slides it where they want. This means some simple symbols or no instructions at all will be required for use. This will allow the product to be used in many different locations by many people.

Societal Factors: The user will be able to do their work efficiently and easily, since they have now more options for changing the positioning of handle. In addition, the user will be able to set the handle further from the disc and/or hold the grinder more securely for some jobs, thereby increasing safety.

Economic Factors: This new design will cost slightly more to produce than the current design because extra machining will have to be done in order to create the track and add the spring. This cost will not be significant compared to the total price of the grinder, and therefore should not adversely affect sales.

Environmental Factors: This revision will not use significantly more material or energy, and therefore should not change the environmental impact of this product.

Advantages and Disadvantages

This design revision will significantly increase the control the user has over the product during regular operation. By adjusting the handle to an appropriate angle the user no longer has to settle for the "One size fits all" construction. In addition, while the current handle locations are useful for cutting material, other tasks such as sanding or removing weld seams can be awkward. By introducing a adjustable handle we will allow the user to move the handle out in front of the angle grinder and have precise two-hand control of the product. This revision will also pair nicely with the changeable gearbox revision, as more handle options may prove to be necessary once new gearbox attachments are developed.

There are two primary disadvantages this system will have over the current design. First, there will be the aforementioned cost increase. The magnitude of this increase will depend on the machining costs for the handle track and the increase in the amount of material used. Given the relative size of this material to the rest of the angle grinder, we do not expect this cost increase to be very severe. The more important disadvantage, will be the increased likelihood of component failure. If the handle is not secured in a hole on the track before grinding begins, the user will most likely snap the handle off because only the spring will be supporting it. In addition, we will have to find some way to cover the handle track during regular use to prevent dust and debris from building up in the holes (essentially causing the previous problem). We will have to look into ways to protect the component from failure (a dust cover system, possible motor cut-off when handle is not in a slot) before this revision can be implemented.

Attachment Connections

For one of our design revisions, we are changing the way the grinding wheels and other attachments connect to the angle grinder. This method will accomplish two things. It will make it faster and easier to change the grinding wheels and other attachments. It will also make grinding easier because there will be no clamp nut in the middle of the grinding wheel, meaning more of the wheel can be used to grind materials.

In the current design, a backing flange is slid over the shaft coming out of the gearbox. The grinding wheel is then slid on and the clamp nut is screwed on to secure the grinding wheel in place.

In our new design, there will be two hooks that connect to loops on the back of the grinding wheel. There will be two buttons that when pressed bring the hooks closer together, allowing the grinding wheel to be put on or taken off. (See figures below for clarification) The new design will be made of aluminum.

Revisions-Top View.jpg
Revisions-Side View.jpg

GSEE Factors

The new design for connecting attachments will address both societal and economic factors.

Global Factors:

  • This design revision will not have a significant impact on any global factors.

Societal Factors:

  • The user will be able to change attachments quicker and easier.
  • Since there will be no clamp nut on the outside of the grinding wheel, the user will have an easier time grinding materials because the entire face of the grinding wheel can be used.

Economic Factors:

  • The cost of the angle grinder and attachments will increase slightly, but is justified by the benefits this new system will provide.
  • Because this attachment method will not allow current grinding wheels and other attachments to be used, consumers must buy DeWalt attachments, thus increasing the profits made from selling this type of angle grinder.

Environmental Factors:

  • The new system will result in less waste because almost all of the material on each grinding disc will be used, instead of having some leftover amount that is disposed of each time.
Advantages and Disadvantages

This design revision will have several advantages for the user, which will translate into additional sales for the company:

  • The new system will allow the entire disc to be used during grinding. This reduction in waste will cut overall cost for grinding a given amount of material.
  • With the clamp nut out of the way, the user will be able to hold the grinder parallel to the surface they are grinding, increasing control and precision.
  • There will be no wear to permanent parts (namely, the clamp nut) caused by the grinding surface during regular usage.
  • The user will not have to touch any hot parts to change discs.

There are only two significant disadvantages to this redesign, both of which are offset by other factors:

  • The new design will only allow the newly designed discs to be used with our product. However, this disadvantage will be offset by DeWalt (or any manufacturer they sell the patent to) being the only suppliers of the new discs, thereby increasing market holdings in teh grinder disc industry.
  • The new discs will be slightly more expensive to make because each disc will have more grinding material (where the hole is in the current design)and it will cost money to add hook-loops to the back of each disc. We expect this cost increase to be offset by the increased longevity of each disc, effectively reducing the cost of grinding a given amount of material because each new disc will last longer than its current counterpart.


  • Title:1800 Mechanical Movements, Devices and Appliances Author: Gardner D. Hiscox

Links to Other Gates


Gate 1

Gate 2

Gate 3